There are many types of current sense amplifiers that output a voltage proportional to a current flowing through a low value sense resistor. The voltage across the resistor is typically referred to as Vsense. The proportion is typically a ratio involving two or more precision resistors.
An ideal current sense amplifier will desirably amplify a small, low-frequency Vsense signal in the presence of a large common mode voltage transient without perturbations in gain. In order to accurately process the wanted Vsense signal and reject the unwanted transient, DC precision and high common mode rejection ratios are required. Because the amplifier's input common mode voltage can be high relative to specified operating voltages of circuitry downstream from the current sense amplifier, it is desirable that the sense amplifier's output be level-shifted from the high average input common mode voltage down to a lower system operational voltage.
In many applications, Vsense is not a DC voltage since the current is generated by the closing of switch, and the switch may be operating at a high frequency. Vsense therefore typically has spikes and other transients. Such transients sometimes cause nonlinear behavior in one or more devices in the current sense amplifier, such as saturation and slewing, resulting in inaccurate current sensing. To remove such high frequency transients, RC filters are required at the input. Since the input impedance of the current sense amplifier is typically a low impedance, only small value resistors and large off-chip capacitors can be used in the off-chip filters, adding expense and size to the current sense amplifier.
Differential current sense amplifiers include an inverting leg and a non-inverting leg. If the legs are not perfectly matched, which is typical in an actual device, there will be some offset (error) in the differential output due to the different electrical characteristics of the legs.
What is needed is an accurate current sense amplifier integrated circuit that generates a differential output, has a very stable gain irrespective of the common mode voltage level, uses a small RC filter that can be implemented on-chip to filter out transients, provides a level shifted differential output voltage, and has a differential output voltage does not include an offset.